The present invention relates to color measurement instruments, and more particularly, to spectrophotometers.
Color measurement instruments for many and varied applications are well known. These instruments are used, for example, to determine color consistency in printed material, photographic material, textiles, and plastics. The most comprehensive color measurements are obtained by instruments known as spectrophotometers, which measure the spectral distribution of light and give a percentage reflection or transmission at many segments in the visible color spectrum.
The field of desk top publishing has expanded greatly in recent years, and color output devices such as color printers, plotters, proofers have become widely used. The color output devices are often controlled by computer software, which transmits control signals to the printer defining color to be produced. To assure color quality, it is desirable to be able to calibrate color printers to produce a selected quality of color for printed material produced by a number of different printers. Additionally, data defining a color product may be transmitted to remote locations to be printed by a variety of printers. In order to be able to provide a product of consistent color characteristics, a comparison to a color standard is required. All of these functions require the accurate measurement of many samples of different colors produced on the device. These colors are produced using only a few colorantsxe2x80x94usually cyan (C), magenta (M), yellow (Y), and black (K).
A color measurement instrument, such as a spectrophotometer, includes a color measurement engine having an optical pick-up. Additionally, many instruments include a drive mechanism for moving either the sample or the engine to effect relative movement between the two. The registration of the sample with respect to the engine and the controlled movement of the sample or the engine are critical components in obtaining consistent and accurate measurements. Only small changes in the distance between the sample and the measurement engine can create significant errors and inconsistencies in the color measurement.
Prior color measurement instruments are illustrated in U.S. Pat. No. 5,369,494 issued Nov. 29, 1994 and entitled xe2x80x9cPortable Scanning Colorimeterxe2x80x9d; U.S. Pat. No. 5,118,183 issued Jun. 2, 1992 and entitled xe2x80x9cAutomated Strip Reader Densitometerxe2x80x9d; and U.S. Pat. No. 5,062,714 issued Nov. 5, 1991 and entitled xe2x80x9cApparatus and Method for Pattern Recognition.xe2x80x9d In these units, the sample drive mechanism is located in the base, while the color measurement engine is located in an assembly above the base. Because these two primary components are located in different housings, there is the possibility that sample registration and movement is not as precisely controlled as required for present day measurement. Accordingly, artisans continue to seek improved structures for maintaining improved consistency and accuracy in sample registration and movement.
The aforementioned issues are addressed in the present invention providing improved sample registration and movement within a portable spectrophotometer. The instrument contains a mechanical drive system that transports the sample past the measurement engine in a precise fashion.
First, the spectrophotometer includes a base and an upper assembly supported for floating movement on the base. Both the color measurement engine and the sample drive mechanism are located within the upper assembly. As the sample is drawn between the base and the upper assembly, the upper assembly can float with samples of various and varying thickness. This approach reduces or even eliminates the need for separate tensioning devices within the drive system, such as springs and/or close tolerances.
Second, the drive mechanism includes a plurality of drive wheels, and the base includes a plurality of independently suspended idler rollers, each of which engages and supports one of the drive wheels. The independently suspended rollers flex to accommodate samples of varying and various thicknesses.
In a third embodiment of the invention, the drive rollers are located xe2x80x9cdownstreamxe2x80x9d (in the direction of sample travel) from the color measurement engine. Tension rollers are provided upstream of the color measurement engine to at least partially resist movement of the sample in response to the drive rollers. The tension created within the sample improves its consistent maintenance in a uniform plane and therefore its consistent registration with the color measurement engine.
In a fourth embodiment of the invention, a planar, low-friction media guide is located on the underside of the upper assembly to engage the top surface of the sample. The thickness of the media is approximately the same as the distance that the drive wheels extend from the upper assembly, so that the media guide consistently engages the top surface of the sample. Therefore, the media guide improves the registration of the sample with respect to the color measurement engine; and the media guide assists the upper assembly in riding the top surface of the sample.
In a fifth embodiment, a two-position backer is provided in the base. The backer includes two separate areas with different reflective properties. The backer is readily manually movable so that either of the two areas can be aligned with the optical pickup of the color measurement engine. For example, the two areas may be white light diffusing opal and stable uniform black. In an alternative embodiment, the light diffusing opal may be illuminated for transmissive analysis.
In a sixth aspect of the invention, the spectrophotometer is capable of both reflective and transmissive analysis. A first light source is included within the color measurement engine and is activated only when reflective analysis is desired. A second light source is included within the base, is aligned with the color measurement engine, and is activated only when transmissive analysis is desired.
These and other objects, advantages, and features of the invention will be more readily understood and appreciated by reference to the description and the drawings.